A conventionally known technique for coding video signals of a high pixel rate, such as HDTV (high-definition television) images, is to divide each of the HDTV images into plural regions and to code, using a coding unit (compression-encoder) of a low pixel rate, each of image signals obtained by the division, so that the processing speed is reduced. With this technique, an image coding device which can handle high pixel rates can be provided (refer to Patent Literature 1, for example). FIG. 1 is a block diagram showing the structure of a conventional image coding device 100 of Patent Literature 1.
The image coding device 100 shown in FIG. 1 includes an image signal input terminal 101, a signal division unit 102, a coding unit 108, a signal combining unit 106, and a coded signal output terminal 107. The coding unit 108 includes a first coding unit 103A and a second coding unit 103B.
The image signal input terminal 101 is supplied with an input image signal (video signal) 110 of a high pixel rate. The input image signal 110 of a high pixel rate is, for example, one of sequential signals such as the high-definition signals mentioned above.
The signal division unit 102 generates a first divided image signal 111A and a second divided image signal 111B by horizontally dividing the input image signal 110 into two, for example. For example, when the valid picture frame of the input image signal 110 has 480 lines, each of the first divided image signal 111A and the second divided image signal 1118 is an image signal having 240 lines.
The first coding unit 103A and the second coding unit 103B are encoders handling low pixel rates. The first coding unit 103A generates a first coded signal 112A by compression-coding the first divided image signal 111A. The second coding unit 103B generates a second coded signal 112B by compression-coding the second divided image signal 111B.
Further, when performing motion estimation and motion compensation on an image near the boundary between the first divided image signal 111A and the second divided image signal 111B, the first coding unit 103A uses a locally decoded image which corresponds to a first overlap region 115A and is generated by the second coding unit 103B, whereas the second coding unit 103B uses a locally decoded image which corresponds to a second overlap region 115B and is generated by the first coding unit 103A.
FIG. 2A shows the first divided image signal 111A and the first overlap region 115A. FIG. 2B shows the second divided image signal 111B and the second overlap region 115B.
The first coding unit 103A generates a locally decoded image of the first divided image signal 111A when coding the first divided image signal 111A. In addition, out of the locally decoded image generated, the first coding unit 103A outputs, to the second coding unit 103B, a locally decoded image 113A corresponding to the second overlap region 115B included in a second search range 116B of the second coding unit 103B.
Similarly, the second coding unit 103B generates a locally decoded image of the second divided image signal 111B when coding the second divided image signal 111B. In addition, out of the locally decoded image generated, the second unit 103B outputs, to the first coding unit 103A, a locally decoded image 113B corresponding to the first overlap region 115A included in a first search range 116A of the first coding unit 103A.
Furthermore, the first coding unit 103A uses a locally decoded image corresponding to the first search range 116A when performing the motion estimation and the motion compensation on the first divided image signal 111A. The first coding unit 103A uses the locally decoded image 113B outputted by the second coding unit 103B, as the locally decoded image corresponding to the first overlap region 115A included in the first search range 116A.
Furthermore, the second coding unit 103B uses a locally decoded image corresponding to the second search range 116B when performing the motion estimation and the motion compensation on the second divided image signal 111B. The second coding unit 103B uses the locally decoded image 113A outputted by the first coding unit 103A, as the locally decoded image corresponding to the second overlap region 115B included in the second search range 116B.
The signal combining unit 106 generates an output coded signal 114 of a high pixel rate by combining the first coded signal 112A and the second coded signal 112B converted into signals of a low pixel rate. Then, the signal combining unit 106 outputs the output coded signal 114 to the coded signal output terminal 107. In this manner, the image coding device 100 of Patent Literature 1 provides the image coding device handling high pixel rates by using the first coding unit 103A and the second coding unit 103B which handle low pixel rates.